The invention relates to a method of producing a surfacial marking on a surface of a body of transmissive material, whereby use is made of a laser beam having a wavelength .lambda. to which the material is substantially transparent.
Such a method is known from European Patent Application EP 531 584. In the method therein described, a layer of an assistant material is directly deposited on the surface. This material comprises at least two different species of transition metal ion, which differ in valency and/or atomic number (e.g. Ti.sup.3+ and Ti.sup.4+, or Ti.sup.3+ and Fe.sup.3+). When subsequently irradiated with a laser beam having a wavelength in the range 300-1600 nm, a heated plasma is generated in the assistant material, and this plasma interacts with and locally etches the surface of the transmissive material. After etching has been completed, the layer of assistant material is removed from the surface.